1. Field of the Invention
The Invention is a wind turbine rotor blade assembly for generation of power and is a wind turbine featuring the blade. The Invention is also a method of making the wind turbine rotor blade. The wind turbine rotor blade of the invention is highly reliable and inexpensive to manufacture compared to large prior-technology wind turbine rotor blades.
2. Description of the Related Art
Wind turbines harvest the kinetic energy of the wind and convert that energy into shaft power at a rotating output shaft. The rotating output shaft turns an electrical generator to produce electrical power. For wind turbines of the horizontal type, the blades rotate in a plane of rotation that is on the upwind side or downwind side of a supporting tower and about an axis of rotation that is generally horizontal with the Earth. The rotor of a horizontal-type wind turbine for commercial electrical power generation is large, and can be over 400 feet in diameter. The rotor includes one or more rotor blades. Each rotor blade is shaped as an airfoil. The wind passing over the rotating rotor blade generates lift, impelling the rotor blade to rotate about the axis of rotation.
A wind turbine rotor blade is subject to substantial stresses due to the rotational inertia of the rotor and the moments imparted by the wind and by gravity. The moments imparted by the wind and by gravity acting on the rotor blade vary along the span of the rotor blade and vary with each revolution of the rotor. Gusts, variable wind speeds and inclement weather can place a very high steady and alternating loading on the structures of a wind turbine. Wind turbines also are subject to frequent starting and stopping cycles. Failure of current-technology wind turbine rotor blades is a very real problem for the wind power industry.
Fiberglass is the material of choice for wind turbine rotor blades. During the 1970s, many materials for turbine rotor blade construction were tried, including steel, aluminum and wood. Turbine designers recognized degradation from fatigue as the dominant factor in rotor blade material selection. Fiberglass has come to dominate the industry due to its moderate density and general resistance to degradation from fatigue.
When adopting fiberglass some thirty years ago, the wind power industry also adopted the fiberglass construction techniques of the time. Those techniques were developed by the small boat industry, which was marked by low-volume production using individual molds in which days of lay-up using multiple plys of fiberglass were performed by hand and in which the hull or deck of the small boat remained until the resin in the fiberglass was fully cured. The rotor blade industry still uses these same techniques. The vast majority (88%) of wind turbine rotor blades are constructed by the hand lay-up of fiberglass-reinforced resin. Dry glass fibers in the form of cloth or roving are manually placed in forms by workers, who then infuse the dry glass fibers with resin, either with or without the assistance of vacuum.
This non-automated prior art method of rotor blade construction is slow, imprecise, and not conducive of high-volume blade manufacture. Prior art wind turbine rotor blade construction provides many opportunities for introduction of manufacturing defects, such as improper reduction in the number of the plys of glass fiber along the span of the blade or introduction of foreign object debris. Prior art wind turbine rotor blade manufacture does not allow monitoring and correction of minor defects in internal blade components before those defects cause major blade failures. The prior art method of blade manufacture also requires large and expensive tooling and highly skilled labor.
Prior art turbine rotor blades feature an upper and a lower side that are formed in molds. Upper and lower spar caps are bonded to the upper and lower sides and are joined by shear webs that extend the length of the blade to provide bending stiffness along the length of the blade and to maintain the cross-sectional profile of the blade. When the upper and lower sides of the prior art rotor blade are joined one to the other, the leading and trailing edges are permanently joined.
The prior art joints between the upper and lower spar caps and the upper and lower sides and between the spar caps and the shear web cannot be inspected once the upper and lower sides are bonded, preventing detection of defects. A local defect, such as a void or defect in a bond for the shear web, can propagate along the length of the rotor blade during operation of the rotor blade, causing catastrophic failure. The local defect generally will translate into a rotor blade failure triggered by a precipitating event, such as erosion, a lightning strike, a blade overload or a tower strike.
The Piasecki Aircraft Corporation (‘PiAC’) conducted a root cause analysis of numerous rotor blade failures. The root cause analysis concluded that factory processes and controls in the manufacturing environment of the prior art wind turbine rotor blades caused many of the failures. Other failures were caused by design shortcomings of the prior art rotor blades. Among the manufacturing defects found in the root cause analysis were dry fiber, misaligned fiber layup, core voids and deficient ply build-up in transition sections.
The prior art does not teach the wind turbine, the wind turbine rotor blade, or the method of the Invention.